1. Field of the Invention
This invention relates to a dc motor apparatus with an index signal output.
2. Description of the Prior Art
A dc motor apparatus with an index signal output is used for apparatus using a dc motor which is required to produce a rotational position signal per full revolution of the dc motor.
A prior art dc motor apparatus with an index signal output is disclosed in Japanese patent application provisional publication No. 61-106056. The disclosed dc motor is as follows:
This dc motor generally comprises a stator, a rotor, and a drive circuit. The stator has magnetic sensors for sensing magnetic flux from field magnets provided to a rotor. Coils of the stator are driven by the drive circuit in response to the signals from the magnetic sensors. A magnetic non-continuous portion is provided to one of the field magnets. The dc motor further comprises a detecting circuit for detecting the magnetic non-continuous portion from one of the magnetic sensors to output an index signal.
However, there is a drawback that output signals from such magnetic sensors is unstable due to variation of temperature, ununiformity of sensitivity of the magnetic sensors, and inaccuracy in assembling, etc., so that it is difficult to distinguish the output signal of the sensor indicative of magnetic non-continuous portion from that indicative of other portion.